1. Field of the Invention
The invention relates to a power output device mounted in, for example, a hybrid vehicle that has a plurality of drive sources or the like, and a hybrid vehicle equipped with the power output device. In particular, the invention relates to an improvement in the timing of switching the rotation speed detector adopted to obtain rotation speed information for a driving control of a specific drive source (primer mover), or the like, from one to another of a plurality of rotation speed detectors that can detect the rotation speed of the drive source.
2. Description of the Related Art
A common hybrid drive device for vehicles employs an internal combustion engine, such as a gasoline engine, a diesel engine, etc., and an electric power device, such as an electric motor or a motor-generator, etc., as motive power sources. There are a variety of forms of the combination of an internal combustion engine and an electric power device. For example, the number of the electric power devices employed in a hybrid drive device is not necessarily one, but some hybrid drive devices employ a plurality of electric power devices.
Known hybrid drive devices in which two electric power devices are employed are disclosed in, for example, Japanese Patent Application Publication No. 2002-225578 (JP-A-2002-225578) and Japanese Patent Application Publication No. 2006-250269 (JP-A-2006-250269). In the technologies of these patent applications, an engine and a first motor-generator are mutually linked via a power distribution mechanism that is made up of a single-pinion type planetary gear mechanism. Besides, torque is transmitted from the power distribution mechanism to an output member, and a second motor-generator is linked to the output member via a speed change mechanism (reduction mechanism). Therefore, the output torque of the second motor-generator is applied as assist torque to the output member. The speed change mechanism is constructed by a planetary gear mechanism that can be switched between a direct connection state and a speed reduction state. Therefore, during the direct connection state, the speed change mechanism can apply the torque of the second motor-generator directly to the output member. During the speed reduction state, the speed change mechanism can apply the torque of the second motor-generator to the output member after increasing the torque.
In a vehicle equipped with this type of hybrid drive device, the running of the vehicle can be switched among an engine drive mode in which only the engine is driven, a motor drive mode in which only the motor-generator is used and the motor-generator is driven as an electric motor, and an engine-motor drive mode in which the engine and the motor-generator are both driven, by controlling the driving and stop of the engine and the motor-generator. Betterment in fuel economy, reduction of noise, reduction of exhaust gas, etc., can be achieved. Besides, by controlling the second motor-generator to a power running state and a regenerative state, it is possible to apply positive torque to the output member or apply negative torque to the output member. Furthermore, since the speed reduction state can be set by the speed change mechanism, the second motor-generator can be reduced in torque or reduced in size.
In this type of hybrid vehicle, the output (torque) is controlled by adjusting the electric current supplied to the motor-generator. Therefore, in a situation where the assist in the drive force is provided by operation of the motor-generator, when a gear ratio shifting operation of the speed change mechanism is performed, it is desirable to control the output of the motor-generator so that the shifting operation is smoothly performed without causing a shift shock.
Therefore, the present rotation speed of the motor-generator is compared with a proper post-shift motor-generator rotation speed (target rotation speed) found on the basis of the rotation speed of the output member, the vehicle speed, etc. Then, a feedback control of the supply current to the motor-generator is performed so that the post-shift rotation speed becomes equal to the target rotation speed. Concretely, a sensor for detecting the rotation speed of the motor-generator is disposed, and the foregoing feedback control is performed on the basis of the rotation speed information obtained via the sensor and the rotation speed of the output member. The rotation speed feedback control includes not only the foregoing control, but also a control in which the control is perfumed on the basis of the gradient of change in the rotation speed of the motor-generator (the amount of change in the rotation speed per unit time). Besides, the foregoing feedback control is used not only for the control of the supply current to the motor-generator, but also for the control of the engagement-disengagement timing of brakes (a friction engagement mechanism) provided for performing the shifting operation of the speed change mechanism.
In the construction in which an assist in drive force is provided by operation of the motor-generator as described above, the rotation speed of the motor-generator greatly changes in association with increases and decreases of the needed assist force. Therefore, in order to effectively perform the feedback control, it is necessary to detect the rotation speed of the motor-generator with high accuracy.
In order to meet this need, it is conceivable to selectively use a sensor suitable for the detection in a low rotation speed range and a sensor suitable for the detection in a high rotation speed range. For example, a construction in which a rotation speed detector called “resolver” is used for low rotation speeds and a rotation speed detector called “north marker” is used for high rotation speeds may be cited. For example, in a situation where the rotation speed of the motor-generator is less than 1000 rpm, the detected value from the “resolver” is used to perform the foregoing feedback control. On the other hand, in a situation where the rotation speed of the motor-generator is greater than or equal to 1000 rpm, the detected value from the “north marker” is used to perform the feedback control. That is, as the detected rotation speed value used for the rotation speed control of the motor-generator or the like, the detected value from the “resolver” is utilized when the rotation speed is in a low speed range, and the detected value from the “north marker” is utilized when the rotation speed is in a high speed range.
With such a construction, in a situation where the rotation speed of the motor-generator changes from the low rotation speed range to the high rotation speed range, the feedback control is switched from the feedback control based on the detected value from the “resolver” to the feedback control based on the detected value from the “north marker” during the transition. Likewise, in a situation where the rotation speed of the motor-generator changes from the high rotation speed range to the low rotation speed range, the feedback control is switched from the feedback control based on the detected value from the “north marker” to the feedback control based on the detected value from the “resolver”.
The “resolver” and the “north marker” are different from each other in the principle in the detection of the rotation speed. That is, the “resolver” has a sensing construction that is suitable for the detection in a low rotation speed range, and the “north marker” has a sensing construction that is suitable for the detection in a high rotation speed range. Therefore, the detected values from the two detectors may sometimes be different from each other even when the motor-generator is operating at a fixed rotation speed.
In the case where the gear ratio shifting operation is performed while the rotation speed of the motor-generator remains within one of the low rotation speed range and the high rotation speed range, the feedback control is performed by continuing using the detected values from one of the “resolver” and the “north marker”, and therefore there is no problem.
However, in the case where the rotation speed of the motor-generator changes so that the feedback control is switched from the feedback control based on the detected values from the “resolver” to the feedback control based on the detected values from the “north marker” or so that the feedback control is switched from the feedback control based on the detected values from the “north marker” to the feedback control based on the detected values from the “resolver”, if the shift execution condition of the speed change mechanism is satisfied and the shifting operation is performed, the detected value of the motor-generator rotation speed fluctuates (fluctuates due to the difference between the detected values from the “resolver” and from the “north marker”) during the shifting operation. Therefore, there arises a possibility that it may become impossible to perform a motor-generator rotation speed control or an engagement/release timing control of a friction engagement mechanism in an optimal manner for preventing the shift shock, and a shift shock may result.